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Abstract:

The invention provides an ink composition having at least (A) a
polymerization initiator, (B) an ester or amide of (meth)acrylic acid
having a 1,3-dioxolane ring skeleton or a 1,3-dioxane ring skeleton or
(B') an ester or amide of (meth)acrylic acid having a 1,3-diketone
structure, and (C) a colorant. The invention further provides an inkjet
recording method and a method for producing a planographic printing
plate, each of which includes at least (I) ejecting the ink composition
onto a hydrophilic support and (II) curing the ink composition by
irradiating the ejected ink composition with active radiation so as to
form a hydrophobic image region on the hydrophilic support. The invention
furthermore provides a planographic printing plate formed by the method
for producing a planographic printing plate.

Claims:

1-31. (canceled)

32. An inkjet recording composition comprising an ink composition, the
ink composition comprising: (a) a polymerization initiator comprising an
aromatic ketone or an acylphosphine oxide compound; (b) an ester or amide
of (meth)acrylic acid having a 1,3-dioxane ring skeleton which is
represented by the following formula (B-2) and having a content ratio of
3 to 35% by mass relative to the total mass of the ink composition; (c) a
pigment; and (d) an additional polymerizable compound which is other than
the (b) ester or amide of (meth)acrylic acid having a 1,3-dioxane ring
skeleton: ##STR00015##

33. The inkjet recording composition according to claim 32, wherein the
(d) additional polymerizable compound comprises an acrylate compound, and
the content of the acrylate compound is 30% by mass or more based on the
total mass of the (d) additional polymerizable compound.

34. The inkjet recording composition according to claim 32, wherein the
viscosity of the ink composition at an ejection temperature of from 40 to
80.degree. C. is from 7 to 30 mPas.

35. The inkjet recording composition according to claim 32, wherein the
ink composition further comprises a solvent in an amount of from 0.1 to
3% by mass with respect to the total mass of the ink composition.

38. The inkjet recording composition according to claim 37, wherein the
polyfunctional acrylate monomer or oligomer has a molecular weight of 400
or more.

39. The inkjet recording composition according to claim 32, wherein the
(d) additional polymerizable compound comprises a combination of a
monoacrylate and a polyfunctional acrylate monomer or oligomer.

40. The inkjet recording composition according to claim 39, wherein the
polyfunctional acrylate monomer or oligomer has a molecular weight of 400
or more.

41. The inkjet recording composition according to claim 32, wherein the
surface tension of the ink composition is from 20 to 30 mN/m.

42. The inkjet recording composition according to claim 32, wherein the
ink composition further comprises a sensitizing dye.

43. The inkjet recording composition according to claim 32, wherein the
ink composition further comprises a polymerization inhibitor.

44. The inkjet recording composition according to claim 32, wherein the
content of the (b) ester or amide of (meth)acrylic acid having a
1,3-dioxane ring skeleton is from 4 to 25% by mass relative to the total
mass of the ink composition.

45. The inkjet recording composition according to claim 32, wherein the
ink composition further comprises a surfactant.

Description:

[0001] This is a Continuation of U.S. patent application Ser. No.
12/851,133, which is a Divisional of U.S. patent application Ser. No.
11/646,368 filed Dec. 28, 2006, which claims priority based on JP
2005-380032, filed on Dec. 28, 2005 and JP 2005-380033, filed on Dec. 28,
2005. The entire disclosures of the prior applications are considered
part of the disclosure of the accompanying divisional application, and
are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is related to an ink composition suitable for
inkjet recording, an inkjet recording method, a printed material obtained
by using the inkjet recording method, a planographic printing plate
obtained by using the ink composition, and a method for producing a
planographic printing plate. Specifically, the invention is related to an
ink composition which cures with high sensitivity upon irradiation with
radiation to form a high-quality image and which has high storage
stability, an inkjet recording method, a printed material obtained by
using the ink composition, a planographic printing plate obtained by
using the ink, and a method for producing the planographic printing
plate. The present invention further relates to inkjet apparatuses are
simple and create less noise.

[0004] 2. Description of the Related Art

[0005] Methods for forming an image on an image recording medium such as
paper based on an image data signal include electrophotographic methods,
sublimation-type thermal transfer methods, melt-type thermal transfer
methods, and inkjet methods. In electrophotographic methods, a process of
forming an electrostatic latent image on a photoreceptor drum by charging
and exposure to light is required, and the process makes the system
complicated, resulting in problems of increased production cost and the
like. Thermal transfer methods can be applied to inexpensive apparatuses;
however, the use of ink ribbons increases the running cost and generates
wastes.

[0006] Inkjet recording methods are applicable to inexpensive apparatuses,
and can reduce the running cost. This is because an image is directly
formed by providing ink only to image portions on the support, thereby
improving the efficiency in the use of ink. Further, the ink jet
recording methods generate less noise, and are excellent image forming
methods.

[0007] Ink compositions curable by irradiation with radiation such as
ultraviolet rays, especially inkjet inks (radiation-curable inkjet ink),
are requested to have sufficiently high sensitivity and capability of
forming high-quality images. When the sensitivity of such inks is
heightened, the inks cure efficiently upon application of radiation,
whereby a lot of benefits are provided including reduced electric power
consumption, longer life of radiation generator owing to reduced load,
and prevention of generation of low-molecular substances caused by
insufficient curing. Further, when ink compositions (inkjet inks in
particular) are used for the formation of the image areas on planographic
printing plates, higher sensitivity increases the curing strength of the
image areas, thus achieving higher printing durability.

[0008] Examples of conventionally-proposed ultraviolet-curing ink
compositions include an ink composition using a mixture of a plurality of
monomers possessing different degrees of functionality (for example, see
Japanese Patent Application Laid-Open (JP-A) No. 5-214280). However, in
order to maintain a curing speed with using such an ink composition, it
is inevitable to use a multifunctional monomer in a large quantity and,
for this reason, there is a problem in flexibility of an image after an
ink therein is cured.

[0009] Planographic printing plates have been conventionally manufactured
by using so-called PS plates. The PS plate has a configuration including
a hydrophilic support and a lipophilic photosensitive resin layer. The
planographic printing plates have been manufactured by a method including
image-forming by exposing the photosensitive resin layer imagewise so as
to increase or decrease the solubility of the exposed portion with
respect to an alkali developer and removing a non-image portion by
dissolving. In recent years, however, digital technology in which image
information is processed, stored, and outputted electronically by
computer is becoming more and more popular, and there is a need for a new
image-output method compatible with the digital technology. Particularly,
methods which enable direct production of printing plates without a
treatment using a developer have been investigated, and methods of
directly forming planographic printing plates by using ink compositions
for inkjet recording are under development. The methods of directly
forming planographic printing plates include ejecting, by an inkjet
method or the like, an ink onto a surface of a support imagewise, the
support preferably being hydrophilic, and irradiating activated radiation
so as to cure the ink, in order to obtain a printing plate having a
desired image, which is preferably a hydrophobic image. In order to form
an image portion of a planographic printing plate, it is desirable to
obtain the properties of rapid curing of ink droplets ejected onto a
support without blurring, excellent strength of a cured image, excellent
adherence of a cured image to a support, and excellent flexibility to an
extent that allows for bending of a support when the planographic
printing plate is applied to a printer without incurring damage such as
cracks, and thus ink compositions satisfying these properties are
currently sought after.

[0010] Accordingly, there has been a need for an ink composition which
cures with high sensitivity upon irradiation with activated radiation, is
capable of forming a high-quality image with superior adhesion to a
recording medium, and preferably further has high flexibility, as well as
a need for a method using such an ink composition.

[0011] There has also been a need for a planographic printing plate which
is obtained by using an ink composition which cures with high sensitivity
upon irradiation with activated radiation (, which is preferably
ultraviolet ray) as well as a need for a method for producing such a
planographic printing plate.

SUMMARY OF THE INVENTION

[0012] The present invention has been made in consideration of the above
problems of the conventional techniques. The inventors of the present
invention have conducted intensive study and have devised the use of a
specific polymerizable compound enables obtaining an ink composition
having improved flexibility, increased ejectability, increased
particle-shape storability and increased adherence to a recording medium
so as to achieve the present invention.

[0013] Namely, as one aspect of the invention, the invention provides an
ink composition, comprising: (A) a polymerization initiator; (B) an ester
or amide of (meth)acrylic acid having a 1,3-dioxolane ring skeleton or a
1,3-dioxane ring skeleton, or (B') an ester or amide of (meth)acrylic
acid having a 1,3-diketone structure; and (C) a colorant.

[0014] While the action of the present invention is not clear, it is
considered to be as described below.

[0015] When (B) an ester or amide of (meth)acrylic acid having a
1,3-dioxolane ring skeleton or a 1,3-dioxane ring skeleton is used as a
polymerizable compound in an ink composition, the curing speed of the
composition at the time of exposure is improved. For this reason, even
when the ink composition is constituted by a monofunctional monomer
excellent in curing sensitivity as a major component without adding a
large quantity of a multifunctional monomer, which is useful in
improvement of curing sensitivity, there is no risk of deteriorating the
sensitivity and the influence of addition of a multifunctional monomer on
film properties, such as decreasing the flexibility of the film after
curing, can be suppressed and, as a result, it is thought that the
properties of the cured composition can be improved while maintaining the
sensitivity.

[0016] The mechanism of the action of improvement of the curing speed is
not clear, but it is thought that the polymerizable compound is favorably
aligned for polymerization of the composition by an interaction between
two oxygen atoms existing in the 1,3-dioxolane ring skeleton or the
1,3-dioxane ring skeleton, or that the influence of oxygen in the air,
which is a polymerization inhibitory component, can be reduced due to an
increase in the polarity of the composition by the two oxygen atoms.

[0017] Further, when (B) an ester or amide of (meth)acrylic acid having a
1,3-diketone structure is used as a polymerizable compound in the ink
composition, the curing speed of the composition at the time of exposure
is improved.

[0018] The mechanism of the action of improvement of the curing speed is
not clear but it is thought that, since the polarity of the composition
is increased by the two oxygen atoms existing in the 1,3-diketone
structure, the influence of oxygen in the air, which is a polymerization
inhibitory component, is reduced, or an interaction between polymerizable
compounds caused by the two oxygen atoms exerts an influence. Further, it
is also thought that, since the 1,3-diketone structure can form an
interaction with the materials of a recording medium on which the ink
composition is applied and with, among these materials, an inorganic
material represented by a metal support, such as aluminum, used when
preparing a planographic printing plate using the ink composition,
adhesion to the support is also improved. Since the interaction formed
based on the 1,3-diketone structure, which is effective in improvement of
the curing speed or improvement of adhesion to the support, is not as
strong as that formed based on a protogenic polarity, the impact on
adaptability to an inkjet is small when it is used as a composition for
an inkjet and reduction of flexibility caused by formation of an
interaction after curing can be suppressed and, accordingly, film
properties can be improved without deteriorating the flexibility thereof.

[0019] In a case where a colored image is formed using the ink
composition, the ink composition may further contain a colorant.

[0020] The ink composition of the invention is preferably applicable for
inkjet recording since, when irradiated with radiation, it cures with
high sensitivity, and the flexibility of a film formed on the surface of
the ink is improved. Namely, as one embodiment of the invention, the
invention provides an inkjet recording composition comprising the ink
composition.

[0021] As another aspect of the invention, the invention provides an
inkjet recording method, comprising: (i) ejecting the ink composition
onto a recording medium; and (ii) irradiating the ejected ink composition
with active radiation to cure the ink composition.

[0022] As still another aspect of the invention, the invention provides a
method for producing a planographic printing plate, comprising: (I)
ejecting the ink composition onto a hydrophilic support; and (II) curing
the ink composition by irradiating the ejected ink composition with
active radiation so as to form a hydrophobic image region on the
hydrophilic support.

[0023] As still another aspect of the invention, the invention further
provides a planographic printing plate, being produced by a method
comprising: (I) ejecting an ink composition onto a hydrophilic support;
and (II) curing the ink composition by irradiating the ejected ink
composition with active radiation so as to form a hydrophobic image
region on the hydrophilic support.

DETAILED DESCRIPTION

Ink Composition

[0024] The ink composition of an embodiment according to the invention
contains at least: (A) a polymerization initiator; (B) an ester or amide
of (meth)acrylic acid having one of a 1,3-dioxolane ring skeleton and a
1,3-dioxane ring skeleton or (B') an ester or amide of (meth)acrylic acid
having a 1,3-diketone structure; and (C) a colorant.

[0025] The ink composition according to the invention can favorably be
used for inkjet recording.

[0026] Hereinafter, components essential to the ink composition according
to the invention are sequentially described.

(B) Ester or Amide of (Meth)Acrylic Acid Having One of a 1,3-Dioxolane
Ring Skeleton and a 1,3-Dioxane Ring Skeleton

[0027] Hereinafter, an ester or amide of (meth)acrylic acid having either
a 1,3-dioxolane ring skeleton or a 1,3-dioxane ring skeleton
(hereinafter, appropriately referred to as (B) specific polymerizable
compound) is described in detail.

[0028] Any compound can be used as the (B) components as long as it is an
ester or amide of (meth)acrylic acid having a 1,3-dioxolane ring skeleton
or a 1,3-dioxane ring skeleton. Examples of the ester or amide of
(meth)acrylic acid having the 1,3-dioxane ring skeleton include a
compound represented by the following Formula (I), and examples of the
ester or amide of (meth)acrylic acid having the 1,3-dioxolane ring
skeleton include a compound represented by the following Formula (II).

##STR00001##

[0029] In Formulae (I) and (II), each of R1 to R8 independently represents
a hydrogen atom or a hydrocarbon group. At least one of R1 to R8 in
Formula (I) and at least one of R1 to R6 in Formula (II) respectively
have a structure of an ester or amide of (meth)acrylic acid as a
substituent at a terminal thereof.

[0030] When one or more of R1 to R8 represent(s) hydrocarbon groups, such
hydrocarbon groups are preferably those each having from about 1 to about
18 carbon atoms and, specific examples thereof include an alkyl group, an
aryl group, an aralkyl group, an alkenyl group and a cycloalkyl group.
Among these, an alkyl group is preferable.

[0031] When one or more of R1 to R8 represent(s) alkyl groups, the alkyl
groups are preferably straight-chain or branch-chain alkyl groups each
having from about 1 to about 8 carbon atoms and, among these,
straight-chain alkyl groups each having from 1 to 4 carbon atoms are more
preferable, and a methyl group or an ethyl group is particularly
preferable.

[0032] The structure of the ester or amide of (meth)acrylic acid which, in
Formula (I), at least one of R1 to R8 and, in Formula (II), at least one
of R1 to R6 have at an end thereof as a substituent is preferably a
monovalent organic group represented by the following Formula (III) or
(IV):

##STR00002##

[0033] In Formulae (III) and (IV), R9 represents a hydrogen atom or a
methyl group and, from the standpoint of reactivity and flexibility of a
polymer to be generated by a polymerization reaction, a hydrogen atom is
preferable. R10 has the same scope as those of the above-described
R1 to R8, and R10 preferably represents a hydrogen atom.
The mark * as used in Formulae (III) and (IV) indicates a position to be
linked with any one of R1 to R8 in Formulae (I) and (II).

[0034] The structure of the ester or amide of (meth)acrylic acid is
preferably a monovalent organic group represented by Formula (III) from
the standpoint of viscosity of the composition and properties thereof
after cured.

[0035] The ester or amide of (meth)acrylic acid existing as a substituent
at each terminal of R1 to R8 in Formula (I) and R1 to R6 in Formula (II)
preferably exists in a number of one or two in a molecule and more
preferably one in a molecule from the standpoint of viscosity of the
compound or properties of the cured composition.

[0036] Among these (B) specific polymerizable compounds, an ester or amide
of (meth)acrylic acid having a 1,3-dioxane ring skeleton is preferable
from the standpoint of a curing speed, and a compound represented by
Formula (I) having one monovalent organic group represented by Formula
(III) in the molecule is particularly preferable.

[0037] While specific examples of such esters or amides of (meth)acrylic
acid each having a 1,3-dioxolane ring skeleton or a 1,3-dioxane ring
skeleton are described below as exemplary compounds (B-1) to (B-16), the
present invention is by no means limited thereto. Further, when
stereoisomers are present in these exemplary compounds, any one of these
stereoisomers may be used and mixtures thereof may also be used in the
invention.

##STR00003## ##STR00004##

[0038] A content of the (B) specific polymerizable compound in the ink
composition of an embodiment of the invention is in a range of 3 to 35%
by mass and, more preferably in a range of 4 to 25% by mass on the basis
of the total mass of the ink composition from the standpoints of a
balance between a curing speed and an adhesion to the substrate and an
inkjet adaptability of the ink composition.

[0039] The (B) specific polymerizable compounds may be used singly or in a
mixture of two types or more.

(B') Ester or Amide of (Meth)Acrylic Acid Having a 1,3-Diketone Structure

[0040] Hereinafter, an ester or amide of (meth)acrylic acid having a
1,3-diketone structure (hereinafter, appropriately referred to as (B')
specific polymerizable compound) is described in detail.

[0041] Any compound can be used as the (B') component as long as it is an
ester or amide of (meth)acrylic acid having a 1,3-diketone structure. Any
structure can be used as the 1,3-diketone structure as long as it has a
carbon atom at each end of adjacent three carbons is in a carbonyl form.
The carbon atom in the center of the adjacent three carbon atoms is
preferably a methylene group (--CH2--) having no substituent.

[0042] It is necessary that the adjacent three carbon atoms which
constitute the 1,3-diketone structure are bonded to an organic group
having an ester or amide of (meth)acrylic acid. An atom or an atomic
group which is adjacent to the adjacent three carbon atoms which
constitute the 1,3-diketone structure may each be a hetero atom such as
an oxygen atom or a nitrogen atom and may come to form an ester bond, an
amide bond or the like in the end together with the atom or the atomic
group adjacent to the carbonyl group of the 1,3-diketone. From the
standpoint of flexibility of the cured composition or a mutual
interaction with the support, the 1,3-diketone structure in the (B')
compound is preferably not contained in a ring structure. Namely, in a
preferable embodiment, the 1,3-diketone structure in the (B') compound
exist outside of a ring structure.

[0043] The number of the structure derived of (meth)acrylic acid which is
present in a molecule of the ester or amide of (meth)acrylic acid having
the 1,3-diketone structure may be one or more. The number of the
structure derived of (meth)acrylic acid is preferably in a range of 1 to
6, and is more preferably 1 or 2. In a particularly preferable
embodiment, the ester or amide of (meth)acrylic acid having the
1,3-diketone structure is an ester or amide of a monofunctional
(meth)acrylic acid having one structure which is derived of (meth)acrylic
acid.

[0044] Preferable examples of the ester or amide of (meth)acrylic acid
having a 1,3-diketone structure include a compound represented by the
following Formula (I').

##STR00005##

[0045] In Formula (I'), R11 represents a hydrogen atom or a methyl
group. From the standpoint of reactivity and flexibility of a polymer to
be generated by a polymerization reaction, R11 preferably represents
a hydrogen atom.

[0046] X represents an oxygen atom or NR12. From the standpoint of
improvement of mobility in the periphery of a polymerizable portion, X
preferably represents an oxygen atom. R12 represents a hydrogen atom
or an alkyl group. R12 preferably represents a hydrogen atom or an
alkyl group having from 1 to 4 carbon atoms, and more preferably
represents a hydrogen atom.

[0047] Z1 represents a single bond or a divalent organic group. When
Z1 represents a divalent organic group, a number of atoms which are
contained in the divalent organic group and are other than hydrogen atoms
is preferably in a range of 1 to 7. More specific examples thereof
include an alkylene group having about 1 to about 7 carbon atoms. Any
single methylene group (--CH2--) or a group of a plurality of
adjacent methylene groups in the alkylene group may be substituted by
substitutent(s) such as a divalent organic group having an unsaturated
bond such as an arylene group or an alkenyl group, a divalent organic
group having a hetero atom or a halogen atom such as a carbonyl group, a
hydroxymethylene group, an alkoxymethylene group, an aminomethylene group
or a halogenated methylene group, an oxygen atom, a sulfur atom or the
like. Among such organic groups, an alkylene group having from 1 to 7
carbon atoms or a group in which a methylene group at one terminal is
substituted with an oxygen atom are particularly preferable as the
divalent organic group represented by Z1. In a preferable
embodiment, the divalent organic group represented by Z1 is bonded
to the 1,3-diketone structure via an oxygen atom. Namely, X, that is the
atom adjacent to Z1 and links Z1 with the 1,3-diketone
structure, is preferably an oxygen atom.

[0048] Z2 represents a monovalent organic group. Z2 is
preferably a hydrocarbon group. More specifically, examples of the
hydrocarbon group represented by Z2 include an alkyl group having
about 1 to 12 carbon atoms and an aryl group having about 1 to 12 carbon
atoms. Among these, an alkyl group having from 1 to 8 carbon atoms is
more preferred, and a methyl group is particularly preferred.

[0049] Specific examples of the ester or amide of (meth)acrylic acid
having a 1,3-diketone structure which can be favorably used in the
present invention include the following exemplary compounds (B'-1) to
(B'-9). Among these compounds, the compounds (B'-1) to (B'-6) are
preferred, and (B'-1) or (B'-2) are particularly preferred.

[0050] It is noted that the invention is by no means limited thereto.

##STR00006##

[0051] A content of the (B') specific polymerizable compound in the ink
composition of an embodiment is in a range of 3 to 45% by mass and, more
preferably in a range of 4 to 35% by mass relative to the total mass of
the ink composition from the standpoint of a balance between the curing
speed and adhesion to the substrate and inkjet adaptability of the ink
composition.

[0052] The (B') specific polymerizable compounds may be used singly or in
a mixture of two or more thereof.

[0053] (A) Polymerization Initiator

[0054] The ink composition according to the invention further contains a
polymerization initiator. Any conventionally-known polymerization
initiator can be appropriately selected and used as the polymerization
initiator of the ink composition of the invention in accordance with
kinds of polymerizable compounds used therewith and utilization purposes
of the ink composition. It is preferable that the polymerization
initiator used in the invention is a radical polymerization initiator.

[0055] The polymerization initiator used in the ink composition of the
invention is a compound which generates a polymerization initiation
starter upon absorbing external energy. The external energy is roughly
classified into heat, to which thermal polymerization initiators are
applied, and radiation ray, to which photopolymerization initiators are
applied. Examples of the radiation ray include γ-rays, β-rays,
electron beams, ultraviolet rays, visible rays, and infrared rays.

[0056] Any conventionally-known thermal polymerization initiators and
photopolymerization initiators can be used in the invention.

[0058] The radical polymerization initiator may be used singly or in
combination of two or more thereof in the invention.

[0059] The (A) polymerization initiator used in the invention is
preferably contained in a range of 0.01 to 35% by mass, more preferably
in a range of 0.1 to 30% by mass, and still more preferably in a range of
0.5 to 30% by mass on the basis of a total amount of the above-described
(B) and (B') components. Alternatively, when the component of the (B) or
(B') specific polymerizable compound is used in combination with a
compound of (D) additional polymerizable compound which is an arbitrary
component to be described below, the content ranges are calculated on the
basis of an entire amount of the polymerizable compounds.

[0060] Further, it is appropriate that the (A) polymerization initiator is
contained in the ink composition so that a mass ratio of an amount of the
polymerization initiator to an amount of an (E) sensitizing colorant
described below becomes in a range of 200:1 to 1:200, preferably in a
range of 50:1 to 1:50, and more preferably in a range of 20:1 to 1:5.

[0061] The ink composition according to the invention may further contain
one or more other components in addition to the above required components
as long as they do not impair the effects of the invention.

[0062] Explanations regarding these other components are provided
hereinafter.

[0063] (D) Additional Polymerizable Compounds

[0064] In addition to the (B) or (B') specific polymerizable compound, the
ink composition according to the invention may further contain an (D)
additional polymerizable compound which is other than the (B) or (B')
specific polymerizable compound. Examples of such additional compound
that can be used in combination with the (B) or (B') specific
polymerizable compound include radical polymerizable compound and
cation-polymerizable compound. The (D) additional polymerizable compound
may be appropriately selected and used in consideration of desired
characteristics and a relationship with the (A) polymerization initiator.

[0065] In the invention, a total content of the polymerizable compounds,
namely, a total content of the (B) or (B') component and a total content
of the (D) additional polymerizable compound which can be simultaneously
used therewith is in a range of 45 to 95% by mass, and preferably in a
range of 50 to 90% by mass on the basis of the mass of the total content
of the ink composition according to the invention.

[0066] Further, in the ink composition according to the invention, the
content of the (B) or (B') component is preferably 7% by mass or more,
more preferably 10% by mass or more, and further preferably 15% by mass
or more on the basis of the total content of the polymerizable compounds
(namely, the total content of the (B) or (B') component and the total
content (D) component) contained in the ink composition.

[0067] Explanations regarding the additional polymerizable compound which
can be used in the invention are provided hereinafter.

[0068] The radical-polymerizable compound is a compound having a
radical-polymerizable ethylenic unsaturated bond, and may be any compound
as long as it has at least one radical-polymerizable ethylenic
unsaturated bond in the molecule. The chemical form of the compound may
be a monomer, oligomer, polymer, or the like. The radical-polymerizable
compound may be used singly or in combination of two or more thereof with
an arbitrary mixing ratio for improving desired properties. It is
preferable that two or more multifunctional compounds are used in
combination in view of controlling the reactively and the properties such
as physical properties.

[0070] Specific examples thereof include esters or amides of acrylic acid
such as 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate,
cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate,
bis(4-acryloxypolyethoxyphenyl)propane (having a weight average molecular
weight of more than 360), polyethylene glycol diacrylate (having a weight
average molecular weight of more than 360), polypropylene glycol
diacrylate (having a weight average molecular weight of more than 360),
dipentaerythritol tetraacrylate, trimethylol propane triacrylate,
oligoester acrylate, N-methylol acrylamide, diacetone acryloamide, or
epoxyacrylate; esters or amides of methacrylic acid such as methyl
methacrylate, n-butyl methacrylate, allyl methacrylate, glycidyl
methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate,
polyethylene glycol dimethacrylate (having a weight average molecular
weight of more than 360), polypropylene glycol dimethacrylate (having a
weight average molecular weight of more than 360), or
2,2-bis(4-methacryloxypolyethoxyphenyl)propane (having a weight average
molecular weight of more than 360); and esters or amides of an allyl
compound such as allyl glycidyl ether, diallyl phthalate, or triallyl
trimellitate. More specifically, radical polymerizable or crosslinkable
monomers, oligomers and polymers commercially available or known in the
art are also usable, such as those described in Shinzo Yamashita Ed.,
"Crosslinking Agent Handbook", (1981, Taisei Publishing); Kiyoshi Kato
Ed., "UV-EB Curing Handbook (Raw Material)" (1985, Kobunshi Kankokai);
RadTech Japan Ed., "Application and Market of UV-EB Curing Technology",
p. 79, (1989, CMC); and Eiichiro Takiyama, "Polyester Resin Handbook",
(1988, Nikkankogyo Shimbun), the disclosures of which are incorporated
herein by reference.

[0071] Examples of the radical-polymerizable compound which may be used in
the invention further include photo-curing polymerizable compounds used
in the photopolymerizable compositions described in JP-B No. 7-31399 and
JP-A Nos. 7-159983, 8-224982, 10-863, and 9-134011.

[0073] Among these vinyl ether compounds, from the standpoint of
curability, adhesion property, and surface hardness, divinyl ether
compounds and trivinyl ether compounds are preferable, and divinyl ether
compounds are particularly preferable. The vinyl ether compounds may be
used singly or in combination of two or more thereof in accordance with
necessity.

[0074] Examples of the additional polymerizable compound further include
(meth)acrylic acid esters such as a (meth)acrylic monomer, a
(meth)acrylic prepolymer, an epoxy monomer, an epoxy prepolymer, an
urethane monomer or an urethane prepolymer (hereinafter arbitrarily
called as an acrylate compound). Specific examples of such additional
polymerizable compound include compounds described below.

[0076] These acrylate compounds are preferable since they are
polymerizable compounds conventionally used in UV curable inks as they
are less irritative or less sensitizing to skin (having small inductivity
of rashes on the skin) and can provide a stable ink-ejecting property
with a relatively low viscosity as well as a good polymerization
sensitivity and a good adhesion to a recording medium.

[0077] Even though these monomers described as the (D) additional
polymerizable compounds have a low molecular weight, each of them has a
low sensitizing property, a high reactivity, a low viscosity, and an
excellent adhesion to the recording medium.

[0078] From the viewpoint of improving sensitivity, resistance to
bleeding, and adhesion property to recording media, it is preferable to
additionally use, as a component (D), a combination of the monoacrylate
and either a polyfunctional acrylate monomer or oligomer having a
molecular weight of 400 or more (preferably 500 or more).

[0079] It is particularly preferable to use a combination of a
monoacrylate monomer selected from the above, a component selected from
the (B) specific polymerizable compound, and either the polyfunctional
acrylate monomer or the polyfunctional acrylate oligomer in an ink
composition used for recording to flexible recording media such as PET
films or PP films, because such a combination can further improve the
adhesion to recording media by providing flexibility to a film formed by
the ink composition while increasing a strength of the film.

[0080] In a particularly preferable embodiment of the invention uses a
combination of three kinds of polymerizable compound (, namely, a
monofunctional acrylate monomer, a bifunctional acrylate monomer, and a
polyfunctional acrylate monomer having tri- or higher-functionality).
Such a combination provides improvements in the sensitivity, resistance
to bleeding, and adhesion to recording media while securing safety.

[0081] The monoacrylate is preferably stearyl acrylate, isoamyl acrylate,
isomyristyl acrylate, or isostearyl acrylate since they provide high
sensitivity and low shrinking property to prevent curling, as well as
preventing bleeding and odor of printed materials and reduction of cost
of an irradiation apparatus.

[0082] In the invention, when any one of the acrylate compounds as
described above is used as the (D) additional polymerizable compound, an
amount of the acrylate compound is preferably 30% by mass or more, more
preferably 40% by mass or more and, still more preferably 50% by mass or
more based on a total mass of the additional polymerizable compound(s)
(namely, a total amount of the (D) component). Further, all of the (D)
additional polymerizable compounds to be simultaneously used can be
selected from among the above-described acrylate compounds.

[0083] The selection of the polymerization initiator and the polymerizable
compound in the invention may be done in accordance with various purposes
such as the prevention of the deterioration in sensitivity caused by the
light-shielding effect of the colorant used in the ink composition. For
example, the ink composition may contain a combination of the radical
polymerizable compound and the radical polymerization initiator.
Alternatively, the ink composition may be formed as a radical-cation
hybrid curable ink using both of the combination of the radical
polymerizable compound and the radical polymerization initiator and a
combination of a cation-polymerizable compound and a cation
polymerization initiator.

[0084] There is no particular restriction to the cation-polymerizable
compound used in the invention as long as it starts a polymerization
reaction upon acid generated by a photo-acid generating agent so as to be
cured, and various cation-polymerizable monomers known as
photo-cation-polymerizable monomers can be used as the
cation-polymerizable compound in the invention. Examples thereof include
the epoxy compounds, vinyl ether compounds, and oxetane compounds such as
those described in JP-A Nos. 6-9714, 2001-31892, 2001-40068, 2001-55507,
2001-310938, 2001-310937 or 2001-220526, the disclosures of which are
incorporated herein by reference.

[0085] Examples of the cation-polymerizable compound which may be used in
the invention further include conventionally-known polymerizable
compounds used for photo-curing resins of cation-polymerization system.
For example, the polymerizable compounds described in JP-A Nos. 6-43633
or 8-324137 can be used as the polymerizable compounds applied to
photo-curing resins of photocation polymerization system sensitized in
the wavelength range of visible rays of 400 nm or more.

[0086] Examples of a cationic polymerization initiator (photolytically
acid-generating agent) to be usable in combination with the cationically
polymerizable compound include a chemical amplification-type photo resist
or a compound used for light cationic polymerization (Japanese Research
Association for Organic Electronics Materials Ed., "Organic Materials for
Imaging" (published by Bun-Shin Shuppan (1993), pp. 187 to 192).
Preferable examples of the cationic polymerization initiators used in the
invention will be described below.

[0088] Secondly, a sulfone compound which generates a sulfonic acid can be
mentioned.

[0089] Thirdly, a halogenide which generates hydrogen halide can also be
used.

[0090] Fourthly, an iron allene complex can be mentioned.

[0091] These cationic polymerization initiators as described above may be
used singly or in a mixture thereof.

[0092] (C) Colorant

[0093] While it is not specifically required to form a colored image in
such a case where the ink composition of the invention is used for
forming an image portion of a planographic printing plate, a colorant may
be added to the ink composition of the invention for purposes such as
improving visibility of a formed image portion or forming a colored image
by using the ink composition.

[0094] While the colorant to be used is not particularly limited, (C-1)
pigments and (C-2) oil-soluble dyes are preferable due to their
resistance against weathering as well as color reproductivity, and may be
arbitrarily selected from known colorants such as soluble dyes. The
colorant used in the ink composition according to the invention
preferably does not function as a polymerization inhibitor in the
polymerization reaction, which is the curing reaction, so that the curing
reaction with active rays is not inhibited.

[0095] (C-1) Pigment

[0096] The pigment for use in the invention is not particularly limited,
and examples thereof include organic or inorganic pigments having the
following Color Index numbers:

[0103] Hereinafter, the oil-soluble dye for use in the invention will be
described.

[0104] The oil-soluble dye for use in the invention is a dye that is
substantially insoluble in water. Specifically, the oil-soluble dye has a
solubility in water at 25° C. (the weight of the dye soluble in
100 g of water) of 1 g or less, preferably 0.5 g or less, and more
preferably 0.1 g or less. Thus, the oil-soluble dye means a so-called
water-insoluble pigment or an oil-soluble colorant, and among them, an
oil-soluble colorant is preferable.

[0105] When the oil-soluble dye used in the present invention is a yellow
dye, the yellow dye is not particularly limited. Examples thereof
include: aryl- or heteryl-azo dyes having a coupling component such as a
phenol, a naphthol, an aniline, a pyrazolone, a pyridone, or an
open-chain active methylene compound; azomethine dyes having a coupling
component such as an open-chain active methylene compound; methine dyes
such as benzylidene dyes and monomethine oxonol dyes; quinone dyes such
as naphthoquinone dyes and anthraquinone dyes; as well as quinophtharone
dyes, nitro-nitroso dyes, acridine dyes, and acridinone dyes.

[0106] When the oil-soluble dye used in the present invention is a magenta
dye, the magenta dye is not particularly limited. Examples thereof
include: aryl- or heteryl-azo dyes having a coupling component such as a
phenol, a naphthol, or an aniline; azomethine dyes having a coupling
component such as a pyrazolone or a pyrazolotriazole; methine dyes such
as arylidene dyes, styryl dyes, merocyanine dyes, and oxonol dyes;
carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes, and
xanthene dyes; quinone dyes such as naphthoquinones, anthraquinones, and
anthrapyridones; and fused polycyclic dyes such as dioxazine dyes.

[0107] When the oil-soluble dye used in the present invention is a cyan
dye, the cyan dye is not particularly limited. Examples thereof include
azomethine dyes such as indoaniline dyes, indophenol dyes, and dyes
having a pyrrolotriazole as the coupling component; polymethine dyes such
as cyanine dyes, oxonol dyes, and merocyanine dyes; carbonium dyes such
as diphenylmethane dyes, triphenylmethane dyes, and xanthene dyes;
phthalocyanine dyes; anthraquinone dyes; aryl- or heteryl-azo dyes having
a coupling component such as a phenol, a naphthol, or an aniline; and
indigo thioindigo dyes.

[0108] The dye may develop a color (yellow, magenta, or cyan) only after
the dissociation of a part of its chromophore. At dissociation, the
counter cation may be an inorganic cation such as an alkali metal or
ammonium, or an organic cation such as a pyridinium or a quaternary
ammonium salt; or a polymeric cation having, as a partial structure, a
cation selected from those described above.

[0110] The oil-soluble dye may be used singly or in combination of two or
more thereof in the invenion.

[0111] Another colorant such as other water-soluble dyes, other disperse
dyes or other pigments may also be additionally used in the invention in
such a range of an amount that does not inhibit the effects of the
inbvention.

[0113] After addition to the ink composition or the ink composition for
ink jet recording according to the invention, the colorant for use in the
invention is preferably dispersed in the ink to a suitable degree.
Various dispersing machines, such as ball mills, sand mills, attriters,
roll mills, agitators, Henschel mixers, colloid mills, ultrasonic wave
homogenizers, pearl mills, wet jet mills, or paint shakers, may be used
for dispersion of the colorant.

[0114] In an embodiment, a dispersant is added at dispersing the colorant.
The dispersant is not particularly limited, and is preferably a polymer
dispersant. The polymer dispersant may be selected, for example from
SOLSPERSE series products manufactured by Zeneca. A synergist suitable
for the pigment may be used as a dispersion aid. In the present
invention, the dispersant and the dispersion aid are added preferably in
an amount of 1 to 50 parts by weight with respect to 100 parts by weight
of the colorant.

[0115] The colorant may be directly added to the inkjet composition
together with other components. Alternatively, the colorant may be, in
advance, added and uniformly dispersed to or dissolved in a solvent or a
dispersing medium such as the (B) or (B') specific polymerizable compound
used in the invention or the other (D) additional polymerizable compound
which is used if desired, so as to improve the dispersibility.

[0116] In the invention, the colorant is preferably compounded by being
added to one or a mixture of two or more of the (B) or (B') specific
polymerizable compound(s) in advance in view of the prevention of the
occurrence of problems such as the deterioration in solvent resistance
caused by the remaining solvent in the cured image and VOCs (volatile
organic compounds) caused by the residual solvent. The polymerizable
compound to be used is preferably a monomer with a lowest viscosity, from
the point of dispersion efficiency only.

[0117] These colorants may be suitably selected and used singly or in
combination of two or more thereof depending on a utilization purpose of
the ink composition.

[0118] In a case where a colorant which exists in a form of a solid
material in the ink composition in the invention, the average diameter of
the particles of the colorant is preferably set in the range of 0.005 to
1.5 μm, more preferably in the range of 0.01 to 1.2 μm, and still
more preferably in the range of 0.015 to 0.1 μm by selection of the
colorant, the dispersant, the dispersion medium, the dispersing
conditions, and the filtration conditions. By controlling the particle
diameter, it becomes possible to prevent clogging in head nozzles and to
maintain favorable storage stability, transparency, and curing efficiency
of the inkjet composition.

[0119] While the content of colorant in the ink composition is
appropriately selected in accordance with utilization purposes, in
consideration of physical properties and coloring property, it is
generally preferably from 1 to 20% by weight, more preferably from 2 to
8% by weight, based on the entire weight of the ink composition.

[0120] (E) Sensitizing Dye

[0121] The ink composition according to the invention may contain a (E)
sensitizing dye in order to promote degradation of the (A) polymerization
initiator caused by irradiation of active ray. The sensitizing dye
absorbs a specific active radiation to take an electronically excited
state. The sensitizing dye in the electronically excited state contacts
the polymerization initiator to cause electron transfer, energy transfer,
heat generation, or the like. As a result, the polymerization initiator
undergoes a chemical change to be decomposed, thereby generating radical,
acid, or base.

[0122] Compounds which are adapted to a wavelength of active radiation
which causes generation of a polymerization starter in the (A)
polymerization initiator and used for the ink composition can be used as
the sensitizing dye. In consideration of the application for curing
reactions of general ink compositions, examples of the sensitizing dye
according to the invention include the dyes belonging to the compound
groups listed below as well as having an absorption wavelength in the
wavelength range of 350 to 450 nm.

[0124] More preferable examples of the sensitizing dye include the
compounds represented by any one of the following Formulae (V) to (VIII).

##STR00007##

[0125] In Formula (V), A1 represents a sulfur atom or NR50;
R50 represents an alkyl group or an aryl group; L2 represents a
non-metallic atomic group which forms a base nucleus of the sensitizing
dye together with the adjacent A1 and the adjacent carbon atom; each
of R51 and R52 independently represents a hydrogen atom or a
monovalent non-metallic atomic group, and R51 and R52 may be
bonded with each other to form an acid nucleus of the sensitizing dye;
and W represents an oxygen atom or a sulfur atom.

##STR00008##

[0126] In Formula (VI), each of Ar1 and A2 independently
represents an aryl group, and Ar1 and A2 are linked via the
bonds from L3; L3 represents --O-- or --S--; and W represents
an oxygen atom or a sulfur atom.

##STR00009##

[0127] In Formula (VII), A1 represents a sulfur atom or NR59;
R50 represents an alkyl group or an aryl group; L4 represents a
non-metallic atomic group which forms a base nucleus of the sensitizing
dye together with the adjacent A2 and the adjacent carbon atom; and
each of R53, R54, R55, R56, R57 and R58
independently represents a monovalent non-metallic atomic group.

##STR00010##

[0128] In Formula (VIII), each of Ar3 and A4 independently
represents --S--, --NR62-- or --NR63--; each of R62 and
R63 independently represents a substituted or non-substituted alkyl
group or a substituted or non-substituted aryl group; L5 represents
a non-metallic atomic group which forms a base nucleus of the sensitizing
dye together with the adjacent A3 and the adjacent carbon atom;
L6 represents a non-metallic atomic group which forms a base nucleus
of the sensitizing dye together with the adjacent A4 and the
adjacent carbon atom; and each of R60 and R61 independently
represents a hydrogen atom or a monovalent non-metallic atomic group, and
R60 and R61 may be bonded with each other to form an aliphatic
ring or an aromatic ring.

##STR00011##

[0129] In Formula (IX), R66 represents an a aromatic ring which may
have a substituent or a hetero ring which may have a substituent; A5
represents an oxygen atom, a sulfur atom or ═NR67; and each of
R64, R65 and R67 independently represents a hydrogen atom
or a monovalent non-metallic atomic group, and each of the pair of
R67 and R64 and the pair of R65 and R67 may be bonded
with each other to form an aliphatic ring or an aromatic ring.

[0130] Specific preferable examples of the compounds represented by any
one of Formulae (V) to (IX) is shown below, while the invention is not
limited thereby.

##STR00012## ##STR00013## ##STR00014##

[0131] (F) Cosensitizer

[0132] In one embodiment, the ink composition according to the present
invention may further contain a cosensitizer. The cosensitizer has
functions of improving the sensitivity of the sensitizing dye to the
active radiation, suppressing the polymerization inhibition by oxygen,
and the like.

[0133] Examples of the cosensitizer include amines such as those described
in M. R, Sander et al., "Journal of Polymer Society" vol. 10, p. 3173,
(1972), JP-B No. 44-20189, JP-A Nos. 51-82102, 52-134692, 59-138205,
60-84305, 62-18537, and 64-33104 or Research Disclosure 33825 (the
disclosures of which are incorporated herein by reference); and specific
examples thereof include triethanolamine, ethyl p-dimethylaminobenzoate,
p-formyldimethylaniline, p-methylthiodimethylaniline, and the like.

[0134] Other examples of the cosensitizer include thiols and sulfides,
such as thiol compounds described in JP-A No. 53-702, JP-B No. 55-500806,
or JP-A No. 5-142772 (the disclosures of which are incorporated herein by
reference), or disulfide compounds described in JP-A No. 56-75643 (the
disclosure of which is incorporated herein by reference). Specific
examples thereof include 2-mercaptobenzothiazole, 2-mercaptobenzoxazole,
2-mercaptobenzimidazole, 2-mercapto-4(3H)-quinazoline, and
β-mercaptonaphthalene.

[0135] Yet other examples of the cosensitizer include amino acid compounds
(e.g., N-phenylglycine), the organic metal compounds described in JP-B
No. 48-42965 (e.g., tributyltin acetate), the hydrogen donors described
in JP-B No. 55-34414, the sulfur compounds described in JP-A No. 6-308727
(e.g., trithiane), the phosphorus compounds described in JP-A No.
6-250387 (e.g., diethyl phosphite), and the Si--H and Ge--H compounds
described in Japanese Patent Application No. 8-65779.

[0136] (G) Other Components

[0137] The ink composition according to the invention may further contain
other components in accordance with necessity. Examples of such
additional components include polymerization inhibitors, solvents, and
the like.

[0138] A polymerization inhibitor may be added to the ink composition
according to the invention for improvement in storability. When the ink
composition according to the invention is applied to inkjet recording, it
is preferable to heat the composition to a temperature in the range of 40
to 80° C. so as to reduce the viscosity of the ink before
ejection; and thus, the addition of a polymerization inhibitor is
preferable for the prevention of the head clogging by thermal
polymerization. The polymerization inhibitor is preferably added in an
amount of 200 to 20,000 ppm with respect to the total amount of the ink
composition according to the invention.

[0140] Considering that the ink composition according to the invention is
a radiation-curable ink composition, the composition preferably contains
no solvent, so that the reaction occurs immediately after deposition to
cure the ink composition. The ink composition may contain a predetermined
solvent as long as it does not affect the curing speed of ink composition
and the like. The solvent may be an organic solvent or water. In
particular, an organic solvent may be added for improvement in
adhesiveness to the recording medium (support such as paper). Addition of
an organic solvent is effective for the prevention of the problem of
VOCs. The amount of organic solvent is, for example, in the range of 0.1
to 5% by weight, preferably in the range of 0.1 to 3% by weight, with
respect to the total weight of the ink composition according to the
invention.

[0141] In addition, other known compounds may be added to the ink
composition according to the invention in accordance with necessity.
Examples of such additional compounds include a surfactant, a leveling
additive, a matting agent, and a resin for adjustment of film physical
properties, such as a polyester resin, a polyurethane resin, a vinyl
resin, an acrylic resin, a rubber resin, or a wax. Further, addition of a
tackifier that does not inhibit polymerization is also preferable in view
of the improvement in adhesiveness to recording media such as polyolefin
or PET. Specific examples thereof include the high-molecular weight
adhesive polymers described in JP-A No. 2001-49200, pp. 5 to 6 (e.g.,
copolymers of a (meth)acrylic ester of an alcohol having an alkyl group
having 1 to 20 carbon atoms, copolymers of a (meth)acrylic ester of an
alicyclic alcohol having 3 to 14 carbon atoms, and copolymers of a
(meth)acrylic ester of an aromatic alcohol having 6 to 14 carbon atoms),
and low-molecular weight adhesive resins having polymerizable unsaturated
bonds.

Properties of Ink Composition

[0142] The ink composition of the invention can be preferably used as an
ink for ink jet recording. Preferable properties in such an embodiment is
herein explained.

[0143] Considering the ejection efficiency when applied to inkjet
recording, the ink composition according to the invention preferably has
an ink viscosity of 7 to 30 mPas, more preferably 7 to 25 mPas, at the
temperature at the time of ejection (e.g., a temperature in the range of
40 to 80° C., more preferably in the range of 25 to 50°
C.). The viscosity at room temperature (25 to 30° C.) of the ink
composition may be 35 to 500 mPas, preferably 35 to 200 mPas.

[0144] It is preferable to adjust and determine the composition properly
so that the viscosity falls in the range. By setting the viscosity at
room temperature high, it become possible to prevent penetration of the
ink into the recording medium even when a porous recording medium is
used, to reduce the amount of uncured monomer and the odor, to suppress
bleeding upon the deposition of ink droplets, and consequently to improve
the image quality.

[0145] The surface tension of the ink composition according to the
invention is preferably from 20 to 30 mN/m and more preferably from 23 to
28 mN/m. When the ink is used for recording on various recording media
such as polyolefin, PET, coated paper, and non-coated paper, the surface
tension is preferably 20 mN/m or more in view of the prevention of
bleeding and penetration, and 30 mN/m or less in view of the wettability.

Inkjet Recording Method

[0146] Hereinafter, the inkjet recording method according to the invention
and inkjet recording apparatuses applicable thereto will be described.

[0147] The inkjet recording method according to the invention comprises
ejecting the ink composition as an ink for ink jet recording onto a
recording medium such as a support or a recording material and curing the
ejected ink composition by irradiation with active radiation rays so as
to form an image on the recording medium.

[0148] Namely, the inkjet recording method according to the invention
comprises (i) ejecting the ink composition of the invention onto a
recording medium and (ii) curing the ejected ink composition by
irradiation with active radiation rays.

[0149] The inkjet recording method of the invention forms an image by
curing the ink composition on the recording medium by including at least
the above-described (i) and (ii).

[0150] The (i) ejecting in the recording method of the invention may
utilize the inkjet recording apparatus that is hereinafter explained in
detail.

Inkjet Recording Apparatus

[0151] The inkjet recording apparatus for use in the invention is not
particularly limited, and may be selected from commercially available
inkjet recording apparatuses. That is, in the invention, the (i) ejecting
of the ink composition on the recording media can be performed by any
known inkjet recording apparatuses including commercially available ones.

[0152] Examples of usable inkjet recording apparatuses include an
apparatus which has at least an ink-supplying system, a temperature
sensor, and active radiation source.

[0153] The ink-supplying system includes, for example, a stock tank
storing the inkjet recording ink according to the invention, a supply
pipe, an ink-supplying tank immediately before inkjet head, a filter, and
a piezoelectric inkjet head. The piezoelectric inkjet head can be
operated such that the ejection is conducted at a resolution in a range
of, for example, 320×320 to 4,000×4,000 dpi, preferably in a
range of 400×400 to 1,600×1,600 dpi, and more preferably in a
range of 720×720 dpi, to form multi-sized dots in an amount in a
range of 1 to 100 pl, which is preferably in a range of 8 to 30 pl. The
unit "dpi" in the invention means the number of dots per 2.54 cm.

[0154] As described above, the temperature of the radiation-curable ink at
the time of ejection is preferably maintained constant. Therefore, the
region from the ink-supplying tank to the inkjet head is preferably
thermally insulated and heated. The method of controlling the temperature
is not particularly limited. In an embodiment, each piping unit is
monitored by multiple temperature sensors and is heated to control the
temperature adequately based on the flow rate of ink and the
environmental temperature. The temperature sensors may be disposed in the
ink-supplying tank and near the nozzles of the inkjet head. In addition,
the head unit to be heated is preferably thermally shielded or insulated
so as to minimize the environmental influence on the apparatus. It is
preferable to insulate the head unit from other units and reduce the heat
capacity of the entire unit to be heated in order to shorten the start-up
time needed for heating or in order to reduce the loss in heat energy.

[0155] When the ink composition or inkjet recording ink composition
according to the invention is ejected onto the surface of the hydrophilic
support, it is preferable to descrease the viscosity of the ink
composition to 7 to 30 mPas (more preferably 7 to 20 mPas) by heating the
ink composition to 40 to 80° C. (more preferably 25 to 50°
C.) before ejection. The use of an ink composition whose ink viscosity at
25° C. is in the range of 35 to 500 mPs is preferable since
significant effects are obtained. In this manner, it is possible to
realize highly stable ejection.

[0156] Generally, radiation-curable ink compositions, such as the ink
composition according to the invention, are usually more viscous than
aqueous inks, and the fluctuation in the viscosity of radiation-curable
ink compositions caused by the fluctuation in temperature during printing
is larger. The fluctuation in the viscosity of ink composition exerts
significant influences on the droplet size and the droplet ejection
speed, causing deterioration in image quality, and thus, it is necessary
to keep the temperature of the ink composition as constant as possible
during printing. It is preferable to control the ink composition
temperature within ±5° C. from the set temperature, more
preferably ±2° C. from the set temperature, and still more
preferably ±1° C. from the set temperature.

[0157] The (ii) curing the ejected ink composition by irradiation with
active radiation rays in the recording method of the invention is
hereinafter explained.

[0158] The ink composition ejected on the surface of a recording medium is
cured by irradiation with active radiation. This is because the (A)
polymerization initiator contained in the ink composition according to
the invention is decomposed by irradiation of active radiation so as to
generate a polymerization starter such as a radical, an acid or a base,
and the function of the polymerization starter is exhibited so as to
cause and promote radical polymerization of the (B) or (B') specific
polymerizable compound, which may further be copolymerized with the (C)
other additional polymerizable compound which are used in combination in
accordance with necessity. In a case where an (E) sensitizing dye
coexists with the (A) polymerization initiator, the (E) sensitizing dye
is excited to the excited state by absorption of active radiation, and
then the (A) polymerization initiator in the polymerization initiation
system is promoted to decomposing upon contact with the (E) sensitizing
dye in the excited state, so as to achieve curing of the ink composition
with high sensitivity.

[0159] Examples of the active radiation include α-rays,
γ-rays, electron beams, X-rays, ultraviolet rays, visible rays, and
infrared rays. The peak wavelength of the active radiation depends on the
absorption characteristics of the sensitizing dye in the ink composition,
and it may be, for example, in a range of 200 to 600 nm, preferably in a
range of 300 to 450 nm, and more preferably in a range of 350 to 420 nm.

[0160] A polymerization initiating system provided in the invention is
sufficiently sensitive to radiation even at a low output. Accordingly,
output of the radiation may be, for example, an irradiation energy of
2,000 mJ/cm2 or lower, preferably from 10 to 2,000 mJ/cm2, more
preferably from 20 to 1,000 mJ/cm2, and still more preferably from 50 to
800 mJ/cm2.

[0161] The active radiation may be irradiated such that the illuminance on
the exposure plane is, for example, in a range of 10 to 2,000 mW/cm2, and
preferably in a range of 20 to 1,000 mW/cm2.

[0162] Mercury lamps, gas or solid state lasers and the like are widely
used as active radiation ray sources, and mercury lamps and metal halide
lamps are widely used for UV-curing inkjet. However, under the current
strong needs for the elimination of the use of mercury from the viewpoint
of environmental protection, it is very important industrially and
environmentally to replace mercury lamps with GaN-type semiconductor
UV-emitting devices. In addition, LED's (UV-LED) and LD's (UV-LD) are
smaller in size, longer in lifetime, higher in efficiency, and lower in
cost, and thus, attracting attention as light sources for
radiation-curing inkjet printers.

[0163] As described above, a light-emitting diode (LED) or a laser diode
(LD) may be used as the active radiation ray source. An ultraviolet LED
or an ultraviolet LD may be used when an ultraviolet ray source is
required. For example, a purple LED having a main emission spectrum in
the wavelength range of 365 to 420 nm is available from Nichia
Corporation. As to a light having a still shorter wavelength, U.S. Pat.
No. 6,084,250 (the disclosure of which is incorporated herein by
reference) discloses an LED having a main emission spectrum in the
wavelength region of 300 to 370 nm. Other ultraviolet LED's are also
commercially available, and capable of emitting radiations of different
UV ranges. The radiation ray source used in the invention is preferably a
UV-LED, and particularly preferably a UV-LED having a peak wavelength in
the range of 350 to 420 nm.

[0164] The maximum illuminance of LED light on the image recording medium
is preferably from 10 to 2000 mW/cm2, more preferably from 20 to 1000
mW/cm2, and still more preferably from 50 to 800 mW/cm2.

[0165] The ink composition according to the invention may be irradiated
with active radiation rays, for example, for 0.01 to 120 seconds,
preferably for 0.1 to 90 seconds.

[0166] The irradiation condition and the basic irradiation method with the
active radiation are disclosed in JP-A No. 60-132767. Specifically, the
exposure is performed in a so-called shuttle process, i.e., by scanning
with a head unit having an ink-ejecting device and light sources disposed
at both sides of the head unit. The active radiation is irradiated a
certain period (e.g., from 0.01 to 0.5 second, preferably from 0.01 to
0.3 second, and more preferably, from 0.01 to 0.15 second) after ink
deposition. When the time between ink deposition and irradiation is very
short, it is possible to prevent bleeding of the uncured ink deposited on
the recording medium. Further, even when a porous recording medium is
used, ink is exposed to radiation before penetrating deep into the
recording medium where the radiation does not reach, whereby residual
unreacted monomer is reduced to reduce odor.

[0167] The curing of the ink may be conducted with a light source that is
not driven. WO 99/54415 Pamphlet discloses an irradiation method in which
the recording area is irradiated with UV rays by using an optical fiber
or by using a mirror disposed on a side wall of the head unit which
mirror reflects the collimated light. Such curing methods may also be
applied in the inkjet recording method of the invention.

[0168] By employing inkjet-recording methods such as described above, the
dot diameter of the deposited ink can be maintained constant even when
various recording media that are different in surface wettability is
used, thus improving the image quality. In order to obtain a color image
by the inkjet recording method according to the invention, it is
preferable to form images by in an order in which a color having higher
lightness overcoats another color(s) having lower lightness. When color
inks are applied in that order, the radiation rays reaches inks located
at the bottom; therefore, superior curing sensitivity, reduction in the
amount of residual monomer and odor, and improvement in adhesiveness are
achieved. Although it is possible to conduct the irradiation with
radiation after a full-color image is formed, it is preferable to
irradiate the image with radiation after each color ink is deposited, in
view of the acceleration of curing.

[0169] As described above, the ink composition according to the invention
is cured by irradiation with active radiation, whereby a hydrophobic
image is formed on the hydrophilic surface of the support.

Method of Producing a Planographic Printing Plate

[0170] The planographic printing plate of the invention may be formed by a
method which comprises ejecting the ink composition according to the
invention onto a hydrophilic support and curing the ink composition.

[0171] Hereinafter, a method for forming a planographic printing plate
using the inkjet recording method of the invention (namely, the method
for forming a planographic printing plate of the invention), and a
planographic printing plate obtained thereby (namely, the planographic
printing plate of the invention) are explained.

[0172] The planographic printing plate according to the invention has a
hydrophilic support and a hydrophobic region formed on the hydrophilic
support.

[0173] The method for forming the planographic printing plate is
characterized by having at least the following (I) and (II):

[0174] (I) ejecting the ink composition according to the invention onto a
hydrophilic support; and

[0175] (II) curing the ink composition by irradiating the ejected ink
composition with radiation so as to form a hydrophobic image on the
hydrophilic support.

[0176] The planographic printing plate of the invention can be formed in a
similar manner as the inkjet recording method of the invention except
that a support having a hydrophilic surface so as to be preferable as a
support for planographic printing plate is used in place of the recording
medium.

[0177] Planographic printing plates have been conventionally manufactured
by, as described above, imagewisely exposing so-called PS plates, in
which a lipophilic photosensitive resin layer is provided on a
hydrophilic support, and solubilizing or curing the thus obtained exposed
portions so as to form image portions and removing non-image portions by
dissolving.

[0178] In contrast, in the method for forming the planographic printing
plate of the invention, the application of the inkjet recording method
enables to form a hydrophobic image portion by directly ejecting the ink
composition in accordance with digitalized image information and curing
the ink composition. By applying such configuration, the method for
forming the planographic printing plate of the invention enables to form
a planographic printing plate in a easier manner than conventionaly-known
methods for forming a planographic printing plate.

[0179] The planographic printing plate of the invention comprises a
hydrophilic support and a hydrophobic image which is formed by the ink
composition of the invention and is provided on a surface of the
hydrophilic support.

[0180] The hydrophilic support for use in the preparation of the
planographic printing plate according to the invention is not
particularly limited as long as it is a dimensionally stable plate-shaped
support. A support whose surface has hydrophilicity may be used as the
support of the planographic printing plate inconsideration of image
quality of printed matter obtained thereby.

[0181] In a case where a material for forming the support has
hydrophilicity, the material can be directly used as it is. In a case
where a material for forming the support does not have hydrophilicity,
the material can be subjected to hydrophilization treatment.

[0182] Examples of the material for the support include paper, paper
laminated with a plastic material (e.g., polyethylene, polypropylene, or
polystyrene), metal plates (e.g., plates formed of aluminum, zinc, or
copper), plastic films (e.g., films formed of cellulose diacetate,
cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose
acetate butyrate, cellulose nitrate, polyethylene terephthalate,
polyethylene, polystyrene, polypropylene, polycarbonate, and
polyvinylacetal), paper or plastic films laminated with a metal selected
from the above metals, and paper or plastic films on which a metal
selected from the above metals are deposited. Preferable examples of the
support include polyester films and aluminum plates. Among them, aluminum
plates, which are superior in dimensional stability and have relatively
low price, are more preferable.

[0183] When the support is an aluminum plate, the aluminum plate may be a
pure aluminum plate, an alloy plate containing aluminum as the main
component and trace amounts of hetero-elements, or a thin film of
aluminum or an aluminum alloy laminated with plastic. Examples of the
hetero-element contained in the aluminum alloy include silicon, iron,
manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and
titanium. The content of the hetero-elements in the alloy is preferably
10% by weight or less. Although pure aluminum plates are preferable in
the invention, aluminum plates containing trace amounts of
hetero-elements are also usable because it is difficult to prepare
completely pure aluminum due to the problems in refining process. The
composition of the aluminum plate is not particularly limited, and may be
selected from known or commonly-used raw materials.

[0184] The thickness of the support is preferably in a range of 0.1 to 0.6
mm and more preferably in a range of 0.15 to 0.4 mm.

[0185] The aluminum plate is preferably subjected to a surface treatment
such as a surface-roughening treatment or an anodizing treatment before
use. The hydrophilicity of the support and the adhesion between the
image-recording layer and the support are improved by the surface
finishing. Before the surface-roughening treatment, the aluminum plate
may be subjected to a degreasing treatment, for example, with a
surfactant, organic solvent, aqueous alkaline solution, or the like so as
to remove the rolling oil on the surface.

[0186] Various methods may be used for surface roughening of aluminum
plate, and examples thereof include a mechanical surface-roughening
treatment, an electrochemical surface-roughening treatment
(surface-roughening by electrochemically dissolving the surface), and a
chemical surface-roughening treatment (surface-roughening by chemically
dissolving the surface).

[0187] The method for the mechanical surface-roughening may be selected
from methods known in the art such as ball polishing, brush polishing,
blast polishing, and buff polishing may be used. A transfer method may
also be used in which the surface irregularity is imprinted by a roll
having a rough surface during hot rolling of aluminum.

[0188] The electrochemical surface roughening may be performed, for
example, by applying an alternate or direct current to the support in an
electrolyte solution containing an acid such as hydrochloric acid or
nitric acid. A method of using a mixed acid is also usable, such as
described in JP-A No. 54-63902, the disclosure of which is incorporated
herein by reference.

[0189] In accordance with necessity, the aluminum plate after
surface-roughening treatment may be further etched with alkali using an
aqueous solution of potassium hydroxide, sodium hydroxide, or the like.
In accordance with necessity, the etched aluminum plate may be further
neutralized, and the neutralized aluminum plate may be further subjected
to anodizing so as to improve the abrasion resistance.

[0190] The electrolyte to be used for the anodization of the aluminum
plate may be selected from various electrolytes as long as the
electrolyte is capable of forming a porous oxide film. Generally, the
electrolyte may be selected from sulfuric acid, hydrochloric acid, oxalic
acid, chromic acid, and mixed acids thereof. The concentration of the
electrolyte is determined adequately according to the kind of the
electrolyte.

[0191] While the condition of the anodization may be changed according to
the electrolyte to be used, and thus cannot be uniformly specified, in
general, the electrolyte concentration may be in a range of 1 to 80% by
weight; the liquid temperature may be in a range of 5 to 70° C.,
the electric current density may be in a range of 5 to 60 A/dm2; the
voltage may be in a range of 1 to 100 V; and the electrolysis time may be
in a range of 10 seconds to 5 minutes. The amount of the anodic oxide
film to be formed is preferably in a range of 1.0 to 5.0 g/m2 and more
preferably in a range of 1.5 to 4.0 g/m2. In this range, it is possible
to obtain a planographic printing plate with superior printing durability
and scratch resistance of the non-image area.

[0192] The support which has been subjected to a surface treatment such as
described above and which has an anodic oxide film may be used, without
further treatments, as the support to be used in the invention.
Alternatively, the support may be further subjected to other treatments
in accordance with necessity, such as a treatment for expanding or
sealing the micropores in the anodic oxide film described in JP-A Nos.
2001-253181 or 2001-322365 (the disclosures of which are incorporated
herein by reference) and a treatment for imparting hydrophilicity to the
support surface comprising immersing the support in an aqueous solution
containing a hydrophilic compound, so as to further improve the adhesion
of the support to the hydrophobic image, hydrophilicity,
stain-resistance, and the like of the support. The treatments for
expanding or sealing are not limited to those described above, and may be
conducted by any conventionally known methods.

Sealing

[0193] The sealing may be conducted by vapor sealing, sealing only with
fluorozirconic acid, sealing with an aqueous solution containing an
inorganic fluorine compound such as sodium fluoride, sealing with water
vapor provided with lithium chloride, or sealing with hot water.

[0194] Among the methods above, sealing with an aqueous solution
containing an inorganic fluorine compound, sealing with water vapor, and
hot-water sealing are preferable.

Sealing with Aqueous Solution Containing Inorganic Fluorine Compound

[0195] Preferable examples of the inorganic fluorine compound used for the
sealing with an aqueous solution containing the inorganic fluorine
compound include a metal fluoride.

[0197] The concentration of the inorganic fluorine compound in the aqueous
solution is preferably 0.01% by weight or higher, more preferably 0.05%
by weight or higher, in respect of sufficient sealing of micropores in
the anodized film. The concentration of the inorganic fluorine compound
in the aqueous solution is preferably 1% by weight or lower, more
preferably 0.5% by weight or lower, in respect of stain resistance.

[0198] The aqueous solution containing an inorganic fluorine compound
preferably further contains a phosphate compound. When the phosphate
compound is contained in the aqueous solution, the hydrophilicity of the
surface of the anodized film is improved thus improving on-press
developability and stain resistance.

[0199] The phosphate compound is preferably selected from metal phosphates
such as phosphates of alkali metals and phosphates of alkaline earth
metals.

[0201] The combination of the inorganic fluorine compound and the
phosphate compound is not particularly limited. In a preferable
embodiment, the aqueous solution contains sodium fluorozirconate as the
inorganic fluorine compound and sodium dihydrogenphosphate as the
phosphate compound.

[0202] The concentration of the phosphate compound in the aqueous solution
is preferably 0.01% by weight or higher, more preferably 0.1% by weight
or higher, from the viewpoint of improving on-press developability and
stain resistance. The concentration of the phosphate compound in the
aqueous solution is preferably 20% by weight or lower, more preferably 5%
by weight or lower, in respect of the solubility.

[0203] The ratios of the respective compounds in the aqueous solution are
not particularly limited. The ratio by mass of the inorganic fluorine
compound to the phosphate compound is preferably in the range of 1/200 to
10/1, more preferably in the range of 1/30 to 2/1.

[0204] The temperature of the aqueous solution is preferably 20° C.
or higher, more preferably 40° C. or higher, but preferably
100° C. or lower, more preferably 80° C. or lower.

[0205] The pH of the aqueous solution is preferably 1 or higher, more
preferably 2 or higher, while it is preferably 11 or lower, more
preferably 5 or lower.

[0206] The method of sealing with the aqueous solution containing an
inorganic fluorine compound is not particularly limited, and examples
thereof include a dipping method and a spraying method. The method of
sealing may be utilized once or twice or more times, and two or more
kinds of the sealing treatments may be conducted in combination.

[0207] Among the above, the dipping method is preferable for conducting
the sealing. When the dipping method is used in the sealing, a time
length for the sealing is preferably at least 1 second, and more
preferably at least 3 seconds, while it is preferably 100 seconds or
shorter, and more preferably 20 seconds or shorter.

Sealing with Water Vapor

[0208] The sealing using water vapor may be conducted by, for example,
allowing the anodized film to continuously or intermittently contact with
pressurized water vapor or water vapor of atmospheric pressure.

[0209] The temperature of the water vapor is preferably 80° C. or
higher, more preferably 95° C. or higher, but preferably
105° C. or lower.

[0210] The pressure of the water vapor is preferably in the range of from
(atmospheric pressure-50 mmAq) to (atmospheric pressure+300 mmAq). In an
embodiment, the pressure of the water vapor is preferably in the range of
1.008×105 to 1.043×105 Pa.

[0211] The duration of the contact with water-vapor is preferably 1 second
or longer, more preferably 3 seconds or longer, while it is preferably
100 seconds or shorter, more preferably 20 seconds or shorter.

Sealing with Hot Water

[0212] The sealing using hot water may be conducted, for example by
dipping an aluminum plate having an anodized film formed thereon in hot
water. The hot water may contain an inorganic salt (for example, a
phosphate) or an organic salt.

[0213] The temperature of the hot water is preferably 80° C. or
higher, more preferably 95° C. or higher, while it is preferably
100° C. or lower.

[0214] The dipping time is preferably 1 second or longer, more preferably
3 seconds or longer, while it is preferably 100 seconds or shorter, more
preferably 20 seconds or shorter.

[0215] Examples of methods for imparting hydrophilicity usable in the
present invention include: alkali metal silicate methods such as
disclosed in U.S. Pat. Nos. 2,714,066, 3,181,461, 3,280,734, and
3,902,734 (the disclosures of which are incorporated herein by
reference), the methods comprising immersing or electrolyzing the support
in an aqueous solution of sodium silicate or the like; a method disclosed
in JP-B No. 36-22063 (the disclosure of which is incorporated herein by
reference), the method comprising treating the support with potassium
fluorozirconate; and methods such as disclosed in U.S. Pat. Nos.
3,276,868, 4,153,461, and 4,689,272 (the disclosures of which are
incorporated herein by reference), the methods comprising treating the
support with polyvinyl phosphonic acid.

[0216] The support according to the invention preferably has an average
center-line roughness of 0.10 to 1.2 μm. In the range above, desirable
adhesiveness to the hydrophobic image, favorable printing durability, and
favorable staining resistance are realized.

[0218] In the method for forming the planographic printing plate of the
invention, the ink composition of the invention is firstly ejected onto a
hydrophilic support. Similarly to the (i) ejecting of the ink composition
of the invention in the inkjet recording method of the invention, the
method for forming the planographic printing plate of the invention may
be performed by using a conventionally-known inkjet recording apparatus.
The range of the temperature of the ink, the range of the viscosity of
the ink, and the methods for controlling these for ejecting the ink using
the inkjet recording apparatus in the method for forming the planographic
printing plate of the invention are also similar to those of the (i)
ejecting of the ink composition in the inkjet recording method of the
invention. The ejected amount and the size of the ejected droplet are
selected so as to be suitable to printed products to be formed.

[0219] (II) Curing Ink Composition by Irradiating Ejected Ink Composition
with Radiation so as to Form Hydrophobic Image

[0220] The ink composition ejected onto a surface of the hydrophilic
support is cured by irradiation with active radiation ray. Details of the
curing system of the ink composition are similar to that in the (ii)
curing of the ejected ink composition of the invention in the inkjet
recording method of the invention. The source of the active radiation ray
and preferable irradiating condition in the method for forming the
planographic printing plate of the invention are also similar to those of
the (ii) curing of the ejected ink composition of the invention in the
inkjet recording method of the invention.

[0221] The planographic printing plate of the invention can be obtained
via the ejecting and curing so as to form, onto a surface of a
hydrophilic support, a hydrophobic image formed by curing the ink
composition of the invention.

[0222] As described above, by manufacturing a planographic printing plate
by applying the inkjet recording method according to the invention, a dot
diameter of the ink landed on the support can be maitained constant, even
when various kinds of supports for planographic printing plates which are
different in surface wettability from one another, and as a result
thereof, hydrophobic images can be formed with a good precision.

[0223] Further, as described above, the ink composition according to the
invention is cured with active radiation ray with a high sensitivity and
can form a hydrophobic region (hydrophobic image) excellent in adhesion
to the support and the quality of the resultant film.

[0224] From these features, the planographic printing plate according to
the invention provides high image quality and excellent print durability.

[0225] Further, as it would be understood by those skilled in the art, the
ink composition according to the invention can be effectively used not
only for forming an image portion of the planographic printing plate but
also as an ink composition which can be generally used for preparation of
a printed matter and the like as described above.

EXAMPLES

[0226] Hereinafter, the present invention is described in detail with
reference to embodiments, while the present invention is by no means
limited thereby.

[0227] The embodiments described below relate to each of plural colors of
inks for UV inkjet.

Example 1

[0228] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0230] The thus-obtained cyan ink composition was printed on a sheet made
of polyvinyl chloride and exposed to irradiation by passing under a ray
emitted from an ultraviolet lamp (power: 120 W/cm) which was subjected to
an iron-doping treatment at a speed of 40 m/mim. The resulted printed
matter prepared with this ink was evaluated as follows.

[0231] (1) Evaluation of Sensitivity for Curing

[0232] Energy of exposure required for curing the ink composition was
measured by a photo-amount integrating meter (trade name: UV
POWERIVIAP®, manufactured by EIT Inc.). As a value measured thereby is
smaller, the ink composition is evaluated as higher in sensitivity for
curing.

[0233] As a result of the above measuring, the ink composition of Example
1 was observed to require an integrated amount of UV exposure is about
330 mJ/cm2, thus it was confirmed that the ink composition of
Example 1 is cured with high sensitivity.

[0234] (2) Evaluation of Curability

[0235] A curability of the ink composition was evaluated by physically
touching an image portion formed after curing the ink composition of the
printed matter. Specifically, the curability is defined by the existence
of adhesiveness on a surface of a cured film of the image portion.

[0236] As a result of the above evaluation, the ink composition of Example
1 was observed as completely losing adhesiveness, thus it was confirmed
that the ink composition of Example 1 is excellent in curability.

[0237] (3) Evaluation of Adhesiveness to Recording Material

[0238] An adhesiveness of the ink composition to a recording material was
evaluated by a cross hatch test in accordance with ISO 2409 (ASTM D
3359). The cross hatch test was conducted so that the cured film of the
printed matter was cut at an interval of 2.0 mm to give 6 lines in each
of the vertical direction and the horizontal direction so that 25 squares
were formed. An adhesive tape (SCOTCH® 3M600, manufactured by 3M) was
adhered with strength onto the printing faces and rapidly peeled off.
Whether the printed image is peeled off or remaining without being peeled
was evaluated according to the notation of 5B to 1B of the ASTM method.
"5B" is the grade for being evaluated as having most excellent
adhesiveness, while "3B" or higher grades are evaluated as having no
practical problem.

[0239] As a result of the above evaluation, the ink composition of Example
1 was observed as having high adhesiveness, and the grade thereof in the
notation of the ASTM method was classified as 4B.

[0240] (4) Evaluation of Flexibility

[0241] An image was formed on a sheet by the ink composition, and after
the sheet was bended for ten times, a flexibility of the ink composition
was evaluated by observing a degree of cracks generated in a film of the
cured image. The result of the bending test is classified into one of
five grades, in which "5 points" is the grade for being evaluated as
having no crack, while "3 points" or higher grades are evaluated as
having no practical problem.

[0242] As a result of the above evaluation, the ink composition of Example
1 was observed as having only a slight crack which does not affect the
printed image, and the grade thereof in the above criteria was classified
as 3 points.

Example 2

[0243] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a magenta ink for UV inkjet.

[0245] The thus-obtained magenta ink composition was printed on a sheet
made of polyvinyl chloride and exposed to irradiation by passing under a
ray emitted from an ultraviolet lamp (power: 120 W/cm) which was
subjected to an iron-doping treatment at a speed of 40 m/mim. The
resulted printed matter prepared with this ink was evaluated in a similar
manner as for Example 1. The results thereof are shown in the following
Table 1.

Example 3

[0246] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a yellow ink for UV inkjet.

[0248] The thus-obtained yellow ink composition was printed on a sheet
made of polyvinyl chloride and exposed to irradiation by passing under a
ray emitted from an ultraviolet lamp (power: 120 W/cm) which was
subjected to an iron-doping treatment at a speed of 40 m/mim. The
resulted printed matter prepared with this ink was evaluated in a similar
manner as for Example 1. The results thereof are shown in the following
Table 1.

Example 4

[0249] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a black ink for UV inkjet.

[0251] The thus-obtained black ink composition was printed on a sheet made
of polyvinyl chloride and exposed to irradiation by passing under a ray
emitted from an ultraviolet lamp (power: 120 W/cm) which was subjected to
an iron-doping treatment at a speed of 40 m/mim. The resulted printed
matter prepared with this ink was evaluated in a similar manner as for
Example 1. The results thereof are shown in the following Table 1.

Example 5

[0252] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0254] The thus-obtained cyan ink composition was printed on a sheet made
of polyvinyl chloride and exposed to irradiation by passing under a ray
emitted from an ultraviolet lamp (power: 120 W/cm) which was subjected to
an iron-doping treatment at a speed of 40 m/mim. The resulted printed
matter prepared with this ink was evaluated in a similar manner as for
Example 1. The results thereof are shown in the following Table 1.

Example 6

[0255] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0257] The thus-obtained cyan ink was printed on a sheet made of polyvinyl
chloride and, then, exposed to irradiation by passing under a ray emitted
from an ultraviolet lamp (power: 120 W/cm) subjected to an iron-doping
treatment at a rate of 40 m/mim. The resultant printed matter prepared
with this ink was evaluated in a same manner as in Example 1. The results
thereof are shown in the following Table 1.

Comparative Example 1

[0258] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0260] The thus-obtained cyan ink was printed on a sheet made of polyvinyl
chloride and exposed to irradiation by passing under a ray emitted from
an ultraviolet lamp (power: 120 W/cm) which was subjected to an
iron-doping treatment at a speed of 40 m/mim. The resulted printed matter
prepared with this ink was evaluated in a same manner as in Example 1.
The results thereof are shown in the following Table 1.

Comparative Example 2

[0261] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0263] The thus-obtained cyan ink composition was printed on a sheet made
of polyvinyl chloride and exposed to irradiation by passing under a ray
emitted from an ultraviolet lamp (power: 120 W/cm) which was subjected to
an iron-doping treatment at a speed of 40 m/mim. The resulted printed
matter prepared with this ink was evaluated in a similar manner as for
Example 1. The results thereof are shown in the following Table 1.

[0264] As is apparent from Table 1, all of the ink compositions of
Examples 1 to 6 were cured with a high sensitivity and were excellent in
all of evaluation items, namely, curability in image portions, adhesion
to recording media, and flexibility of the formed images, and proved to
be at such a level as having no practical problem.

[0265] In contrast, the ink composition of Comparative Example 1, which
does not contain the (B) component but contains a difunctional acrylate
as a major component, showed a favorable curability but showed an
insufficient adhesion such that the result of cross-hatch test was at a
practically problematic level. Further, the ink composition of
Comparative Example 2, which contained lauryl acrylate in place of the
(B) component, was insufficient in curability, and thus the cured film
thereof was unable to be evaluated.

Example 7

Preparation of Support

[0266] An aluminum alloy containing 0.06% by weight of Si, 0.30% by weight
of Fe, 0.025% by weight of Cu, 0.001% by weight of Mn, 0.001% by weight
of Mg, 0.001% by weight of Zn, and 0.03% by weight of Ti, with its
balance being Al and inevitable impurities, was melted, filtered, and
cast into an ingot having a thickness of 500 mm and a width of 1200 mm in
a DC casting method. Using a surface cutter, its surface was cut off to
an average depth of 10 mm. Then, this was soaked at 550° C. for
about 5 hours, and after its temperature lowered to 400° C., this
was hot-rolled into a sheet having a thickness of 2.7 mm. Then, this was
immediately annealed at 500° C. using a continuous annealing
device, and then cold-rolled into a sheet having a thickness of 0.24 mm.
An average crystalline particle diameter of a shorter diameter of
aluminum in the thus-obtained aluminum plate was 50 μm, and an average
crystalline particle diameter of a longer diameter of aluminum in the
thus-obtained aluminum plate was 300 μm. The aluminum plate was cut to
have a width of 1030 mm, and then processed according to the following
surface-treating processes.

[0267] The following processes (a) to (j) were performed in a succeeding
manner for surface treating. Liquid adhered to the aluminum plate was
removed by a nip roll after each of the following processes and washings.

[0268] (a) Mechanical Surface-Roughening

[0269] Using rotary nylon brush rolls, the surface of the aluminum plate
was mechanically roughened while an abrasive slurry prepared by
suspending an abrasive (silica sand) having a specific gravity of 1.12 in
water was applied thereto. The abrasive had a mean particle diameter of
30 μm and a maximum particle size of 100 μm. The nylon brushes were
made of 6,10-nylon, the length of each nylon hair was 45 mm, and the
diameter thereof was 0.3 mm. The nylon hairs were densely planted in many
holes formed in a stainless cylinder having a diameter of 300 mm to
construct the nylon brushes. Three such rotary nylon brush rolls were
used. Two support rolls (each having a diameter of 200 mm) were disposed
below the brush rolls, spaced from them by 300 mm. The brush rolls were
pressed against the aluminum plate to such a degree that the load of the
power motor to drive the brush rolls increased by 7 kW over the load
thereof to the brush rolls not kept in contact with the aluminum plate.
The direction of the brush rotation was the same as the traveling
direction of the aluminum plate. The number of brush revolutions was 200
rpm.

[0270] (b) Etching with Alkali

[0271] Thus mechanically roughened aluminum plate was etched by spraying
it with an aqueous alkali solution having a sodium hydroxide
concentration of 2.6% by weight and an aluminum ion concentration of 6.5%
by weight at 70° C. An amount of the aluminum plate etched thereby
was 10.0 g/m2. Then, the etched aluminum plate was washed with a
spray of water.

[0272] (c) Desmutting

[0273] Thus etched aluminum plate was desmutted by spraying it with an
aqueous solution of 1 wt. % nitric acid (containing 0.5% by weight of
aluminum ions) at 30° C., and then washed with a spray of water.
The aqueous nitric acid solution used for the desmutting is a waste in a
process of AC electrochemical surface roughening in an aqueous nitric
acid solution.

[0274] (d) Electrochemical Surface-Roughening

[0275] Subsequently, the aluminum plate was electrochemically
surface-roughened at an alternating current voltage of 60 Hz. The
electrolytic solution used is an aqueous nitric acid solution of 10.5
g/liter (containing 5 g/liter of aluminum ions and 0.007% by weight of
ammonium ions), and a temperature thereof was 50° C. A waveform of
an alternating current source used therein was trapezoid, brachymorphic
current having a period from the time that the current value was zero to
the time that the current value leached to a peak was 0.8 msec and a duty
ratio of was 1:1. A carbon electrode was therein used as a counter
electrode. Ferrite was used as a material for an auxiliary anode.

[0276] The current density was 30 A/dm2 as the peak current; and the
quantity of electricity was 220 C/dm2 in terms of the total quantity
of electricity to the aluminum plate serving as an anode. 5% of the
current from the power source was divided to the auxiliary electrode.
Further, the aluminum plate was washed with a spray of water.

[0277] (e) Alkali Etching

[0278] Subsequently, the aluminum plate was further etched by spraying it
with an aqueous alkali solution having a concentration of 26% by weight
of sodium hydroxide and a concentration of 6.5% by weight of aluminum ion
at 32° C. An amount of the aluminum plate etched thereby was 0.50
g/m2. This is performed in order to remove the smut component which
is essentially formed of aluminum hydroxide and is formed in the previous
AC electrochemical surface-roughening treatment, and in order to dissolve
the edges of the pits, which were also formed in the previous treatment,
so as to make the pits smooth. Further, the aluminum plate was washed
with a spray of water.

[0279] (f) Desmutting

[0280] The aluminum plate was again desmutted by spraying it with an
aqueous solution containing 15 wt. % of sulfuric acid (containing 4.5% by
weight of aluminum ions) at 30° C. Next, this was washed with a
spray of water. A waste liquid, which was formed by the electrochemical
surface-roughening using alternating current in the aqueous nitric acid
solution, was used as the aqueous solution containing sulfuric acid in
this desmutting.

[0281] (g) Electrochemical Surface-Roughening

[0282] Subsequently, the aluminum plate was electrochemically
surface-roughened at an alternating current voltage of 60 Hz. The
electrolytic solution used is an aqueous hydrochloric acid solution of
5.0 g/liter (containing 5 g/liter of aluminum ions), and a temperature
thereof was 35° C. A waveform of an alternating current source
used therein was trapezoid, brachymorphic current having a period from
the time that the current value was zero to the time that the current
value leached to a peak was 0.8 msec and a duty ratio of was 1:1. A
carbon electrode was therein used as a counter electrode. Ferrite was
used as a material for an auxiliary anode.

[0283] The current density was 25 A/dm2 as the peak current; and the
quantity of electricity was 50 C/dm2 in terms of the total quantity
of electricity to the aluminum plate serving as an anode. Further, the
aluminum plate was washed with a spray of water.

[0284] (h) Alkali Etching

[0285] Subsequently, the aluminum plate was further etched by spraying it
with an aqueous alkali solution having a concentration of 26% by weight
of sodium hydroxide and a concentration of 6.5% by weight of aluminum ion
at 32° C. An amount of the aluminum plate etched thereby was 0.12
g/m2. This is performed in order to remove the smut component which is
essentially formed of aluminum hydroxide and is formed in the previous AC
electrochemical surface-roughening treatment, and in order to dissolve
the edges of the pits, which were also formed in the previous treatment,
so as to make the pits smooth. Further, the aluminum plate was washed
with a spray of water.

[0286] (i) Desmutting

[0287] The aluminum plate was again desmutted by spraying it with an
aqueous solution containing 25 wt. % of sulfuric acid (containing 0.5% by
weight of aluminum ions) at 60° C. Next, this was washed with a
spray of water.

[0288] (j) Anodic Oxidation

[0289] Subsequently, the aluminum plate was subjected to anodic oxidation,
using a two-stage electrolytic anodic oxidation device. In the device,
the length of the first and second electrolysis units is 6 m each; the
length of the first and second power supply units is 3 m each; and the
length of the first and second power supply electrodes is 2.4 m each. The
electrolyte supplied to the first and second electrolysis units is
sulfuric acid. The electrolyte had a sulfuric acid concentration of 170
g/liter, and contained 0.5% by weight of aluminum ions. Its temperature
was 43° C. Thus processed, the aluminum plate was washed with a
spray of water. The amount of the final oxide film formed was 2.7
g/m2.

Preparation and Evaluation of Planographic Printing Plate

[0290] An image was formed on an aluminum support obtained by surface
treating the aluminum plate as described above by using the ink
composition of Example 1 and cured in a similar manner as in Example 1 so
as to form a planographic printing plate of Example 7.

[0291] The quality of an image obtained by printing with the planographic
printing plate and the printing durability of the planographic printing
plate of Example 7 were evaluated as follows.

Evaluation of Image on Printed Sheet

[0292] The planographic printing plate was set in a printer (trade name:
HEIDEL KOR-D, manufactured by Heidelberg) and printing was performed with
supplying a ink for sheet printing (trade name: VALUES-G (RED),
manufactured by Dai-Nippon Ink Chemical Industry) and dampening water
(trade name: ECOLITY 2, manufactured by Fuji Film Corporation). After 100
sheets were printed thereby, an image on a 100th printed sheet was
visually evaluated. As a result thereof, it was confirmed that the image
on the printed sheet was good with neither an imageless portion in the
image area nor a stain in the non-image area thereof.

Evaluation of Printing Durability

[0293] After the above, the printing operation was continued to observe
that 5,000 sheets or more prints obtained thereby exhibited high quality
with neither an imageless portion in the image area nor a stain in the
non-image area. It was thus confirmed that the planographic printing
plate of Example 7 can be evaluated as having no practical problem.

[0294] As a result thereof, it was found that the planographic printing
plate formed by using the ink composition of the invention is capable of
forming a printed image having a high quality as well as has good
printing durability, and thus the ink composition of the invention can be
preferably used for forming a planographic printing plate.

Example 8

[0295] A cyan ink for UV inkjet of Example 8 was obtained and evaluated in
a similar manner as in Example 1 except that components described below
were used. The results are shown in Table 2.

[0297] The ink composition of Example 8 has a high adhesion, and a value
of the adhesion was evaluated as 3B in accordance with the ASTM method,
which is applicable for practical use.

Example 9

[0298] A magenta ink for UV inkjet of Example 9 was obtained and evaluated
in a similar manner as in Example 2 except that 14.0 parts of the
exemplary compound (B'-2) was used in place of 14.0 parts of the
exemplary compound (B-3). The results are shown in Table 2.

Example 10

[0299] A yellow ink for UV inkjet of Example 10 was obtained and evaluated
in a similar manner as in Example 3 except that 12.0 parts of the
exemplary compound (B'-1) was used in place of 12.0 parts of the
exemplary compound (B-2). The results are shown in Table 2.

Example 11

[0300] A black ink for UV inkjet of Example 11 was obtained and evaluated
in a similar manner as in Example 4 except that 34.0 parts of the
exemplary compound (B'-1) was used in place of 34.0 parts of the
exemplary compound (B-2). The results are shown in Table 2.

Example 12

[0301] A cyan ink for UV inkjet of Example 12 was obtained and evaluated
in a similar manner as in Example 5 except that 32.0 parts of the
exemplary compound (B'-4) was used in place of 32.0 parts of the
exemplary compound (B-2) and, then, a printed matter was obtained. The
results are shown in Table 2.

Example 13

[0302] A cyan ink for UV inkjet of Example 13 was obtained and evaluated
in a similar manner as in Example 6 except that 30.0 parts of the
exemplary compound (B'-3) was used in place of 30.0 parts of the
exemplary compound (B-3) and, also, 3.0 parts of exemplary compound
(B'-4) was used in place of 3.0 parts of exemplary compound (B-14). The
results are shown in Table 2.

Example 14

[0303] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a magenta ink for UV inkjet.

[0305] The thus-obtained magenta ink composition was printed on a sheet
made of polyvinyl chloride and exposed to irradiation by passing under a
ray emitted from an ultraviolet lamp (power: 120 W/cm) which was
subjected to an iron-doping treatment at a speed of 40 m/mim. The
resulted printed matter prepared with this ink was evaluated in a similar
manner as for Example 1. The results thereof are shown in the following
Table 2.

Comparative Example 3

[0306] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0308] The thus-obtained cyan ink composition was printed on a sheet made
of polyvinyl chloride and exposed to irradiation by passing under a ray
emitted from an ultraviolet lamp (power: 120 W/cm) which was subjected to
an iron-doping treatment at a speed of 40 m/mim. The resulted printed
matter prepared with this ink was evaluated in a similar manner as for
Example 1. The results thereof are shown in the following Table 2.

Comparative Example 4

[0309] Components described below were mixed with a high-speed
water-cooled mixer, to thereby obtain a cyan ink for UV inkjet.

[0311] The thus-obtained cyan ink composition was printed on a sheet made
of polyvinyl chloride and exposed to irradiation by passing under a ray
emitted from an ultraviolet lamp (power: 120 W/cm) which was subjected to
an iron-doping treatment at a speed of 40 m/mim. The resulted printed
matter prepared with this ink was evaluated in a similar manner as for
Example 1. The results thereof are shown in the following Table 2.

[0312] As is apparent from Table 2, all of the ink compositions of
Examples 8 to 14 were cured with a high sensitivity and were excellent in
all of evaluation items, namely, curability in image portions and
adhesion to recording mediums, and proved to be at such a level as having
no practical problem.

[0313] On the other hand, the ink composition of Comparative Example 3,
which did not contain the (B') component but contained a difunctional
acrylate as a major component, showed a favorable curability but showed
an insufficient adhesion such that the result of cross-hatch test was at
a level having a practical problem. Further, the ink composition of
Comparative Example 4, which contained lauryl acrylate in place of the
(B') component, was insufficient in curability, and therefore, the cured
film thereof was unable to be evaluated.

Example 15

[0314] A planographic printing plate was prepared and evaluated in a
similar manner as in Example 7 except that the ink composition of Example
8 was used in place of that of Example 1.

[0315] As a result thereof, it was confirmed that the image on the printed
sheet was good with neither an imageless portion in the image area nor a
stain in the non-image area thereof.

[0316] After the above, the printing operation was continued to observe
that 20,000 sheets or more prints obtained thereby exhibited high quality
with neither an imageless portion in the image area nor a stain in the
non-image area. It was thus confirmed that the planographic printing
plate of Example 15 can be evaluated as having no practical problem.

[0317] As a result thereof, it was found that the planographic printing
plate formed by using the ink composition of the invention is capable of
forming a printed image having a high quality as well as has good
printing durability, and thus the ink composition of the invention can be
preferably used for forming a planographic printing plate.

CROSS-REFERENCE TO RELATED APPLICATION

[0318] This application claims priority under 35 USC 119 from Japanese
patent Application Nos. 2005-380032 and 2005-380033, the disclosures of
which are incorporated by reference herein.